Phonograph coupling for radioreceivers



Sept. 8, 1931. A. H. GREBE ET AL PHONOGRAPH COUPLING FOR RADIORECEIVERS Filed June 28, 1950 Qu z]. l

DETECTOR STA 6 4110/0 remuamr AMPL/f/ER Patented Sept. 8, 1931 UNIED: STATES PATENT OFFICE ALFRED H. GREBE, OF HOLLIS, AN D IPERCIVAL D. LOWELL, OF JAMAICA, NEW YORK, AS- SIGNOBS TO A. H. GREBE & 00., ING, OF RICHMOND HILL, NEW YORK, CORPORA- TION OF NEW YORK PHONOGRAPH COUPLING FOR RADIORECEIVERS Application filed June 28,

In the present type of radio receiving set, it is customary to make suitable arrangements so that the signal from a phonographic magnetic pick-up can be suitably amplified and given off by the loud speaker of the radio receiving set. When suitable arrangements for such phonographic reproduction are made, it is advisable to have the set so modified that any radio frequency signal coming from the antenna or other signal gathering device cannot effect the loud speaker. The present invention has to do with a convenient device and arrangement for making this operation possible; several novel and useful features of the invention will become evident when it is described.

In the drawings:

Fig. 1 is a circuit diagram showing the functioning of our device; and

Fig. 2 shows the switch S of Fig. 1, as it is arranged in the set for operation from the movements of the tuning condensers of the radio frequency amplifiers.

In Fig. 1, we have indicated generally the radio frequency amplifier (R. F. A.) of the radio receiver, and the audio frequency amplifier (A. F. A.) of the receiver; the arrangement of the detector is shown in detail. The output of the It. F. A. is supplied to the input circuit of the detector circuit through a small coupling condenser C The input circuit of the detector is generally tuned and in our drawings we have so shown it; our invention is not, however, limited in its application to detector circuits arranged for tuning but is equally applicable to detectors having untuned circuits.

In Fig. 1 of the drawings, the tuned input circuit consists of the inductance coil L, the fixed condenser C (of comparatively large capacity), and the variable tuning condenser Ct. This tuning condenser will generally be mounted for common control with the other tuning condensers of the set. hen the switch S is closed, the input circuit of the detector is seen to consist of L,(l and C in series. When switch S is opened, however, the transformer T is inserted in the circuit thus completely destroying its tuning quality. It follows from this that the de- 1930. Serial No. 464,584.

tector input circuit is practically non-responsiveto any radio frequency signal being recelved by the set.

hen the switch S is open, however, it

age of transformer T. As the output of transformer T is already audio-frequency, no detector action is necessary and none takes place. The detector tube is thus made tobfunction as an audio frequency amplifier tu e.

By those skilled in the art, it will be understood that the wire marked C, which leads to the proper bias voltage for the-detector grid, must have in series with it a comparatively large impedance of some kind, so that the output of transformer T will not be diverted to any great extent, along this path. In one embodiment of our idea, a resistance of one million ohms is put in series with the wire G; in this case practically full output voltage of transformer T is availabllle for exciting the grid of the detector tu e.

Many previous schemes for introducing the phonograph output into the receiver set have introduced this into the input circuit of the first audio frequency triode, but this method is generally unsatisfactory in those modern broadcast receiving sets which employ only one stage of audio frequency amplification.

It will be seen that our arrangement makes available the amplifying action of the detector tube in addition to that of the A. F. A. it-

self, thus increasing the voltage amplification pick-up excitation to the modern broadcast receiver, which frequently has only one stage of audio frequency amplification.

In our preferred form of switch, the process of opening the switch is carried out by the movement of the tuning condensers. As

these approach their extreme position (all W3 out) a lug on the moving plates passes against the upper end of the switch rod, depresses the latter and so opens the switch. As soon as the tuning condensers are turned from their all out position, the spring action of the switch rod automatically closes the switch, short circuiting the phonograph transformer and arranging the detector input circuit forthe normal tuning position.

Having thus described our invention, What We claim is:

1. In a radio receiver having tuning means, a vacuum tube detector, a transformer arranged for excitation from a phonograph pick-up, and means automatically operated by the adjustment of said tuning means to utilize said detector tube as an amplifier of the signals generated by said phonograph pick-up.

2; In a radio receiver, a vacuum tube detector circuit with tuning means, a transformer arranged for excitation from a phonograph pick-up, and means automatically operated by the adjustment of said tuning means to utilize said detector as an amplifier of signals generated by said phonograph pick-up.

3; 111 a radio receiver, a vacuum tube detector with a tunable input circuit, a transformer arranged for excitation from a phonograph pick-up, and an automatic switch movable to one position to close the tunable input circuit and short circuit the transformer and to another position to open the tuned detector input circuit and connect the transformer for exciting the grid of the detector tube,

4'. In a radio receiver, a vacuum tube detector circuit with; tuning means, a transformer arranged for excitation from a phonograph pick-up, and means automatically operatedby the adjustment of the tuning means for modifying the detector circuit as required to connect thetransformer for exciting the grid of the detector tube.

We, aflix our signatures.

ALFRED H. GREBE. PERCI-VAL D. LOWVELL. 

